According to market watcher In-Stat, Vista, as we should now be calling 'Longhorn', will have a "significant impact" on Tablet PC sales.

Tablet PCs have been around for almost three years now, albeit with "mixed success", as In-Stat puts it. Some $1.19bn worth of Tablet PCs were shipped in 2004, and In-Stat reckons that will rise to $5.36bn in 2009.

This year, the researcher estimates, shipments will be worth $1.51bn, as some 825m units ship, a 38.7 per cent increase over the 595m units that shipped last year. This will be despite an 8.8 per cent dip in the average selling price.

From 2006 onwards, the ASP will fall further from around $1,825 now to $1,275 in 2009, In-Stat reckons. That, plus the availability of more Tablet-centric software, along with Windows Vista and "larger form factors that directly address the corporate market" will drive demand, pushing up unit shipments 69.7 per cent in 2006 and a further 85.7 per cent in 2007. Shipment growth with slow to 30.8 per cent and 23.5 per cent in 2009, In-Stat believes.

Again, the big revenue growth will come in the 2006/2007 timeframe after which it will begin to level off through 2008 and 2009.

So far the greatest demand for Tablet PCs has come from vertical markets, which is where all Microsoft's previous attempts to take pen computing into the mainstream have ended up. Tablet PC was heralded by some observers as the version that would at last succeed, but it's clear it's as niche as past stylus-operated Windows devices have been. ®